Fwd: Re: [linux-usb-devel] URB with scatter-gather?

[Oliver Neukum]

Am Dienstag, 18. September 2001 22:20 schrieben Sie:
> > > So... has anyone thought about what it would take for Linux to support
> > > a single URB with multiple scatter-gather elements?
> > >
> > > AFAIK, an URB needs a single continuous memory block for a transfer.
> > > It would be nice if we could use scatter-gather instead.
> > >
> > > Any thoughts?
>
> Shouldn't request queuing be able to solve that problem?  Just
> create one URB per s/g segment (e.g. from the SCSI layer),
> queue, and be done.  It's just a question of which level you
> do the s/g at ... I'd rather keep it out of usbcore, that's quite
> complex enough as it is!!

Isn't that exactly what the "next" field in the URB was defined for ?
The only change needed would be that the callback of the URB is used
only from the last URB. That is the first URB with NULL in the "next" field
or the first URB which happens to fail.

Thus we'd get rid of the overhead of resubmitting the URB from the interrupt
handler.

        Regards
                Oliver

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